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Thread: Dual Zoned HVAC

  1. #1

    Dual Zoned HVAC

    I just bought a two story home with zoned heat/AC. Ceiling in living area, where downstairs thermostat is located, is two stories high. The heat will come on and run for a while, and shut off. A few minutes I hear the furnace
    light up, the blower comes on and runs for 10 seconds before shutting off.
    This goes on all day. I thought it might be a bad thermostat, so replaced it with a new one. Problem still exists. I have tried all sorts of different ideas.
    Is there some trick to setting the upstairs thermostat at a particular degree, and the downstairs at another? This is driving me crazy!

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,723
    better call for service, short cycling is not a good thing.......

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Do you mean the first flloor stat runs the furnace.
    Then after its done, alittle while later the second floor stat runs the furnace for that short tiem period.

    If so.
    Call the installer back, and have him install the stats at better locations.
    Or set the cecond floor stat lower.

    How long have you lived in this house.
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    How many times must one fix something before it is fixed?

  4. #4

    Dual Zone

    Hi Beenthere,
    Thanks for the response.
    There are two separate systems.
    I've been in the house about a month.
    System upstairs works fine. It's the downstairs unit that runs for about 10 minutes and shuts off. A few minutes later, it comes back on and shuts right back off.
    I was wondering if the stat location might have something to do with this.
    In all homes I've lived in, it has always been about 4 feet above the intake.
    Same here, but very high ceiling in this room.

  5. #5
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    is the furnace or burners turning on and then off or is the fan only doing it.

    if the furnace has a fan limit then it is not uncommon for the heat exchanger to build up heat again after shut down and turn the fan on for a few seconds.

    alot of times this can be ajusted out

    have the unit looked at so you dont keep throwing time and money and not solving anything

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    It may be location. Could be the hole behind the stat is not sealed and is leaving cool air come down the joist cavity, and causing the stat to short cycle.

    Need a tech to check it out to find the cause.
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  7. #7
    Join Date
    Mar 2008
    Posts
    59

    Zoning

    I had a similar problem in my own home. Without knowing more specifics I can tell you my experience. With the zoning I have there was a seperate limit sensor installed wired directly to the zone panel. Mine was placed in the wrong spot and when my first floor zone opened alone it would trigger that limit switch and cause the system to short cycle. I am not sure if that is what is happening but you might want to trace where the wires go to and see if one is leading to a temperature limit sensor installed on the ductwork itself. If the sizing is a bit small and you dont have a good dumper/bypass damper installed that might be causing your short cycling. Good luck!!

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